Linear actuator for driving an optical head incorporated in an optical disk

ABSTRACT

In an electro-magnetic actuator, an objective lens is mounted on a lens holder which is elastically supported by two leaf springs and a focusing coil is wound around the lens holder. The lead springs is fixed on a carriage to which tracking coil is also fixed. Guide roller mechanisms are provided on the both sides of the tracking coil and are slidably mounted on guide rails, respectively. The tracking coil are so arranged as to be extended in magnetic gaps of magnetic circuits disposed between the carrier and the guide rails. In each of the magnetic circuit, first and second yokes are so faced to each other as to defined the magnetic gap, a pair of permanent magnets are interposed between the first and second yokes, a third yoke also so faced to the second yoke as to defined the magnetic gap, a pair of permanent magnets are also interposed between the second and third yokes, and a permanent magnet is provide at the first yoke to apply a magnetic flux to the focusing coil.

BACKGROUND OF THE INVENTION

1. 1. Field of the Invention

The present invention relates to an electro-magnetic actuator and anoptical disk apparatus incorporating the same and, more particularly, toa linear actuator for driving an optical head incorporated in an opticaldisk apparatus for reproducing/recording information from/in an opticalrecording medium by converging a laser beam onto the optical recordingmedium.

2. Description of the Related Art

An electro-magnetic actuator as an actuator for driving a head iscurrently widely used in various fields of, e.g., an optical diskapparatus and a magnetic disk apparatus. For example, as anelectro-magnetic actuator for driving an optical head used in an opticaldisk apparatus, a mechanism as shown in FIG. 1 is known. In themechanism shown in FIG. 1, an objective lens 102 for focusing a lightbeam from a light source onto an optical disk 101 is mounted on amovable member 103. The objective lens 102 can be finely moved by ashort distance along its optical axis toward the optical disk 101 andcan be also finely moved by a short distance in the radial direction ofthe optical disk 101 by a mechanism provided in a cove 104 to move theobjective lens. A tracking driving mechanism for driving the objectivelens 102 in the radial direction of the optical disk 101 by acomparatively long distance comprises a pair of magnetic circuits 107each constituted by a yoke 105 and a permanent magnet 106 fixed to theyoke 105, a tracking coil 108 fixed to the movable member 103, linearguides 109 for regulating a moving direction of the movable member 103,and guide rollers 110 which can roll on the linear guides 109. Themovable member 103 is roughly driven in the radial direction of theoptical disk 101 by a Lorentz force generated by a current flowingthrough the tracking coil 108 and magnetic fluxes flowing in themagnetic circuits 107, and the objective lens 102 is finely driven bythe above objective lens driving mechanism to form a light beam spot ata desired position on the surface of the optical disk 101, therebyrecording or reproducing information in or from the optical disk 101.

As shown in FIG. 2, in the magnetic circuit 107 to be incorporated insuch a mechanism, a plate-like yoke 105a and a yoke 105b having asubstantially U-shaped section are connected to form the yoke 105, andthe permanent magnet 106 is fixed on the inner surface of the yoke 105aand arranged in a space between the yokes 105a and 105b.

In the magnetic circuit 107 having the above arrangement, as shown inFIG. 3A, a magnetic path is formed such that not all of magnetic fluxesgenerated by the N pole of the permanent magnet 106 flow straight to thelongitudinal section of the yoke 105b but some magnetic fluxes flowtoward two short sides of the yoke 105b. In addition, as shown in FIG.3B, magnetic fluxes generated by the end portion of the permanent magnet106 form a magnetic path which returns directly to the yoke 105a throughair outside the magnetic circuit. Therefore, a magnetic flux densitydistribution in a magnetic gap is not uniform along the inner surface ofthe yoke 105b but a magnetic flux density at the end portion becomessmaller than that at the center of the magnetic gap.

When the size of the magnetic circuit 107 is decreased, it becomes verydifficult to maintain a uniform magnetic flux density distribution inthe magnetic gap along the inner surface of the yoke 105a due tomagnetic characteristics of the permanent magnet 106 or materialcharacteristics such as magnetic saturation of the yoke 105. As aresult, a considerably large amount of magnetic fluxes leak into airhaving a smaller permeability than that of the yoke 105. When a magneticpath is formed in this manner, magnetic fluxes at the center of themagnetic gap largely differ from those at its end portion. Therefore, ifsuch a magnetic circuit is applied to the electro-magnetic actuatorshown in FIG. 1, a generated driving force changes in accordance withthe position of the movable member 103 and degrades uniformity of movingacceleration of the objective lens 102. As a result, positioning controlof the objective lens 102 becomes unstable.

As described above, a magnetic path formed by the conventional magneticcircuit is not uniform along the inner surface of the magnetic gap, andit is very difficult to maintain uniformity of a magnetic flux densitydistribution in the magnetic gap if the magnetic circuit is made smallerin size. Therefore, if this magnetic circuit is applied to anelectro-magnetic actuator, a generated driving force changes inaccordance with the position of a movable member, resulting in unstablepositioning control of an objective lens.

An optical system of an optical head of the mechanism shown in FIG. 1generally comprises three systems, i.e., a guiding optical system forguiding a light beam from a light source, an optical pick-up system forfocusing the light beam onto an optical disk and picking up the lightbeam from the optical disk, and a detecting system for detecting thelight beam. More specifically, in the guiding optical system, a lightbeam emitted from a light source, e.g., a semiconductor laser is shapedand collimated. In the optical pick-up system, the optical pick-upsystem, the light beam transmitted from the guiding optical system isfocused on a rotating optical disk by the objective lens 102. In thedetecting system, the light beam modulated and reflected by a recordingsurface of the disk is focused on a photodetector and detected forsignal reading and position detection. In the conventional optical headshown in FIG. 1, the guiding optical system and the detecting systemhaving a considerably large total weight (generally 50 g or more) aremounted on the chassis 103 as a movable member. Therefore, in order todrive the optical head at a high speed, the magnetic circuit 107 capableof generating high power, i.e., the magnetic circuit 107 having acomparatively large size is required. In this case, since the size ofthe movable member is naturally increased, further limitations areimposed if the optical head must be housed and operated in a limitedspace in the optical disk apparatus.

Recently, a separate type optical head device shown in FIG. 4 in which aguiding optical system and a detecting system are separated from amovable member to reduce the weight of the movable member and realizehigh-speed driving has been used. In this separate optical head device,a lens bobbin 202 to which an objective lens 102 is connected iselastically supported by parallel leaf springs 204, thereby supportingthe objective lens 102 to move parallel to its optical axis direction (Zdirection). A flat type focusing coil 206 as a focusing driving systemis wound around the side surface of the lens bobbin 202 to have its axisin the Y direction. The focusing coil 206 and a fixed magnetic circuit(not shown) form an electro-magnetic driving system in which a Lorentzforce, i.e., a driving force for driving the objective lens 102 in the Zdirection is generated in accordance with a Fleming's left-hand rule bythe direction (X direction) of a current flowing through the focusingcoil 206 and the direction (Y direction) of magnetic fluxes generated bya permanent magnet of the magnetic circuit. The lens bobbin 20 is movedby this driving force while equally curving the two leaf springs. Thatis, the objective lens 102 is driven in the optical axis direction. Areflecting mirror 240 is arranged below the objective lens 102 todeflect a light beam, emitted from a light source and passed through afixed guiding optical system, through 90° and radiate the deflectedlight beam onto a disk 101. A light beam modulated and reflected by theupper surface of the disk 101 is guided to a detecting optical system bythe reflecting mirror 240.

Guide rollers 110 such a bearings elastically supported by support pins210 are arranged at both side surfaces of a carriage 208 as a movablemember and roll along linear guides 109 with a circular section fixed ona base (not shown) and elongated in the X direction. Therefore, thecarriage 208 is moved in the disk radial direction (X direction) whileits two ends are supported by the linear guides 109. A tracking coil 214is wound around a tracking coil bobbin portion 212 of the carriage 208to have its axis in the X direction. The tracking coil 214 is insertedin a non-contacting state into a magnetic gap between a yoke and thepermanent magnet of the magnetic circuit and forms a voice coil motortogether with the magnetic circuit. This voice coil motor generates aLorentz force, i.e., a driving force for driving the carriage 208 in theX direction by the direction (Y direction) of a current flowing throughthe tracking coil 214 and the direction (Z direction) of magnetic fluxesin the magnetic gap of the magnetic circuit. The carriage 208 is movedby this driving force while the rollers 110 roll on the linear guides109. That is, the objective lens 102 is moved in the X direction.

Of the two conventional optical heads described above, in the opticalhead device shown in FIG. 1 in which both the guiding and detectingoptical systems are mounted on the movable member 103, it is difficultto record/reproduce information at a high speed since reduction inweight of the movable member is limited.

In the separate type optical head device, in order to improve responsecharacteristics upon X-direction driving of the movable member 208, itis preferred to sufficiently narrow the magnetic gap, i.e., move thetracking coil 214 inserted in the magnetic gap as close as possible tothe yoke surface or the magnet surface opposing each other above andbelow the tracking coil 214. In order to allow the guide roller 110 torotate on the linear guide 109 with a low frictional resistance, therotating shaft of the guide roller and the linear guide direction mustbe set to be substantially perpendicular to each other. In addition, inorder to restrict the optical head in a direction except for thetracking direction by a plurality of guide rollers 110, an inclinationand a positional accuracy of each pin 210 for supporting the guideroller 110 must be set within predetermined allowable ranges. Since,however, mounting accuracies of the tracking coil 214 and the movablemember 208 are actually not so high, it becomes difficult to maintain anon-contacting state between the tracking coil 214 and the yoke if themagnetic gap is made narrower. Similarly, since mounting accuracies ofeach pin 210 and the movable member 208 are not so high, it is difficultto set the inclination and positional accuracy of each pin 210 withinallowable ranges.

In order to stabilize optical characteristics and Z-direction driving ofthe objective lens 102, a high mounting accuracy and inclinationaccuracy are required for the lens bobbin 202 or the focusing coil 206.However, a demand for a high mounting accuracy of the focusing coil 206,the tracking coil 214, the lens bobbin 202, the pin 210, the reflectingmirror 240, and the like, and a complicated shape of the separateoptical head cause reduction in productivity in amanufacturing/assembling process of the optical head. The above demandfor a high mounting accuracy of the pin 210, the lens bobbin 202, thefocusing coil 206, and the like in the separate type optical head deviceis similarly present for a mounting accuracy between the movable member103 and the guide roller support pin and between the movable member 103and the optical pick-up 104 in the standard optical head devicedescribed above.

In addition, in order to realize an optical head which can performrecording/reproduction at a high speed in a future, an optical head inwhich a movable member is arranged so as not to produce an unnecessaryvibration in a moving optical element and which can be driven without aninclination or offset of an optical axis by eliminating an unnecessarymass distribution must be developed.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an electro-magneticactuator which can constantly provide a stable driving force.

It is another object of the present invention to provide an optical diskapparatus wherein a beam spot formed on an optical disk by a light beamemerged from an objective lens is precisely controlled.

It is still another object of the present invention to provide anoptical disk apparatus which can achieve a small size, a light weight,and an improved productivity and can be driven at a high speed without avibration and an inclination of an optical axis, thereby performingrecording/reproduction of information at a high speed.

According to the invention, there is provided an apparatus forgenerating a driving force, comprising first and second yokes, havingflat surfaces opposing each other via a gap and arranged in a firstdirection, for allowing magnetic fluxes to pas therethrough; first andsecond plate-like permanent magnets each having surfaces of one andanother poles, separately arranged in the gap in a second directionperpendicular to the first direction, the surface of the one pole beingfixed to the surface of the first yoke, and the surface of the anotherpole being fixed to the surface of the second yoke, the first and secondplate-like permanent magnets supplying magnetic fluxes to the yokes togenerate a magnetic field across the gap in the first direction; anelectro-magnetic coil extending in the gap between the first and secondplate-like permanent magnets, a current being supplied to theelectro-magnetic coil in the gap in a third direction perpendicular tothe first and second directions; and supporting means for supporting theelectro-magnetic coil to move in the second direction, theelectro-magnetic coil being moved in the second direction by a drivingforce generated by an interaction between the magnetic field and thecurrent.

According to the invention, there is also provided an apparatus forgenerating a driving force, comprising a first yoke, having a flatsurface, for passing magnetic fluxes; a second yoke, having one andopposite flat surfaces, the one surface opposing one surface of thefirst yoke via a first gap, and arranged in a first direction, forpassing magnetic fluxes; a third yoke, having one flat surface opposingthe opposite surface of the second yoke via a second gap, and arrangedin the first direction, for passing magnetic fluxes; first and secondplate-like permanent magnets each having surfaces of one and anotherpoles, separately arranged in the first gap in a second directionperpendicular to the first direction, the surface of the one pole beingfixed to the surface of the first yoke, and the surface of the anotherpole being fixed to the one surface of the second yoke, the first andsecond plate-like permanent magnets supplying magnetic fluxes to theyokes to generate a first magnetic field across the first gap in thefirst direction; third and fourth plate-like permanent magnets eachhaving surfaces of one and another poles, separately arranged in thesecond gap in the second direction, the surface of another pole beingfixed to the opposite surface of the second yoke, and the surface of theone pole being fixed to the one surface of the third yoke, the third andfourth plate-like permanent magnets supplying magnetic fluxes to theyokes to generate a second magnetic field across the second gap in thefirst direction; a first electro-magnetic coil extending in the firstand second gaps between the first and second plate-like permanentmagnets, first and second current components being supplied in oppositedirections in the first and second gaps in a third directionperpendicular to the first and second directions; supporting means forsupporting the first electro-magnetic coil to move in the seconddirection, the first electro-magnetic coil being moved in the seconddirection by a first driving force generated by interactions between thefirst magnetic field and the first current component and between thesecond magnetic field and the second current component; magnetic fieldgenerating means, arranged close to one of the first and second yokes,for generating a third magnetic field in the third direction; and asecond electro-magnetic coil held on the supporting means to move in thefirst direction and having a section in which a third current componentis flowed in the second direction, the second electro-magnetic coilbeing moved in the first direction by a second driving force generatedby an interaction between the third magnetic field and the thirdcurrent.

According to the invention, there is further provided a system foroptically reproducing information from an optical recording medium,comprising focusing means for focusing a light beam onto the opticalrecording medium in a first direction; driving force generating meansfor generating a first driving force to convey the focusing means in asecond direction perpendicular to the first direction, the driving forcegenerating means including first and second magnetic circuit meansarranged with an interval therebetween in a third directionperpendicular to the first and second directions, conveyor means forconveying the focusing means in the second direction, and moving meansfor moving the focusing means in the first direction, each of the firstand second magnetic circuit means being constituted by a first yoke,having a flat surface, for passing magnetic fluxes, a second yoke,having one and opposite flat surfaces, the one surface opposing onesurface of the first yoke via a first gap, and arranged in the firstdirection, for passing magnetic fluxes, a third yoke, having one flatsurface, the one surface opposing the opposite surface of the secondyoke via a second gap, and arranged in the first direction, for passingmagnetic fluxes, first and second plate-like permanent magnets eachhaving surfaces of one and another poles, separately arranged in thefirst gap, the surface of the one pole being fixed to the surface of thefirst yoke, and the surface of the another pole being fixed to the onesurface of the second yoke, the first and second plate-like permanentmagnets supplying magnetic fluxes to the yokes to generate a firstmagnetic field across the first gap in the first direction, third andfourth plate-like permanent magnets each having surfaces of one andanother poles, separately arranged in the second gap in the seconddirection, the surface of the another pole being fixed to the oppositesurface of the second yoke, and the surface of the one pole being fixedto the one surface of the third yoke, the third and fourth plate-likepermanent magnets supplying magnetic fluxes to the yokes to generate asecond magnetic field across the second gap in the first direction, andmagnetic field generating means, arranged close to one of the first andsecond yokes, for generating a third magnetic field in the thirddirection, the conveyor means including a first electro-magnetic coilhaving first and second sections extending in the first and secondmagnetic circuits, each of the first and second sections extending inthe first and second gaps between the first and second plate-likepermanent magnets, and first and second current components beingsupplied in opposite directions in the first and second gaps in thethird direction in each of the first and second sections, and firstsupporting means for supporting the first electro-magnetic coil to beconveyed in the second direction, the first electro-magnetic coil beingconveyed in the second direction by a first driving force generated byinteractions between the first magnetic field and the first currentcomponent and between the second magnetic field and the second currentcomponent, and the moving means being constituted by a secondelectro-magnetic coil having a section in which a third current isflowed in the second direction, and second supporting means, held on thefirst supporting means, for supporting the second electro-magnetic coiland the focusing means to move in the first direction, the focusingmeans and the second electro-magnetic coil being moved in the firstdirection by a second driving force generated by an interaction betweenthe third magnetic field and the third current; and optical guide meansfor guiding light beams to the focusing means being conveyed.

According to the invention, there is still further provided an opticalhead assembly for scanning an optical recording medium with a lightbeam, comprising focusing means, having an optical axis, for focusing alight beam onto a surface of the optical recording medium; firstelectro-magnetic coil means for generating a driving force for movingthe focusing means in a first direction along the optical axis;supporting means, having one and the other end portions, for suspendingthe focusing means and the electro-magnetic coil means to move in thefirst direction; a first structure including a first resin portion towhich the electromagnetic coil means and one end portion of thesupporting means are fixed and a second resin portion to which the otherend portion of the supporting means is fixed, the first and second resinportions being integrally molded; second electro-magnetic coil means forgenerating a driving force for moving the first structure in a seconddirection perpendicular to the first direction; and a second structurehaving a third resin portion to which the second electro-magnetic coilmeans is fixed, the third resin portion being integrally molded, thefirst structure being fixed to the second structure, and the first andsecond structures being capable of moving in the second direction.

According to the invention, there is furthermore provided an apparatusfor reproducing information from an optical recording medium, comprisingan optical head assembly for scanning the optical recording medium witha light beam, the assembly including focusing means, having an opticalaxis, for focusing a light beam onto a surface of the optical recordingmedium, first electro-magnetic coil means for generating a driving forcefor moving the focusing means in a first direction along the opticalaxis, supporting means, having one and the other end portions, forsuspending the focusing means and the electro-magnetic coil means tomove in the first direction, a first structure including a first resinportion to which the focusing means, the electro-magnetic coil means,and one end portion of the supporting means are fixed and a second resinportion to which the other end portion of the supporting means is fixed,the first and second resin portions being integrally molded, secondelectro-magnetic coil means for generating a driving force for movingthe first structure in a second direction perpendicular to the firstdirection, a second structure having a third resin portion to which thesecond electro-magnetic coil means is fixed, the third resin portionbeing integrally molded, the first structure being fixed to the secondstructure, and the second structure being capable of moving in thesecond direction, and first and second guide roller mechanisms, fixed tothe second structure, for conveying the second structure; first andsecond guide rails, extending parallel to each other in the seconddirection, for guiding the first and second guide roller mechanisms,respectively; means for generating a magnetic field for causing thefirst electro-magnetic coil to generate a driving force; and means forgenerating a magnetic field for causing the second electro-magnetic coilto generate a driving force.

Additional objects and advantages of the invention will be set forth inthe description which follows, and in part will be obvious from thedescription, or may be learned by practice of the invention. The objectsand advantages of the invention may be realized and obtained by means ofthe instrumentalities and combinations particularly pointed out in theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate presently preferred embodiments ofthe invention and, together with the general description given above andthe detailed description of the preferred embodiments given below, serveto explain the principles of the invention.

FIG. 1 is a perspective view schematically showing a conventionaloptical head apparatus;

FIG. 2 is a perspective view schematically showing a magnetic circuit ofthe optical head apparatus shown in FIG. 1;

FIGS. 3A and 3B are longitudinal sectional views showing the magneticcircuit shown in FIG. 2;

FIG. 4 is a perspective view schematically showing a conventionaloptical head apparatus different from that shown in FIG. 1;

FIGS. 5 and 6 are exploded perspective and perspective views,respectively, showing a magnetic circuit incorporated in an actuatoraccording to an embodiment of the present invention;

FIGS. 7 and 8 are sectional and side views, respectively, schematicallyshowing a magnetic path of the magnetic circuit shown in FIGS. 5 and 6;

FIGS. 9, 10, 11, and 12 are side views each showing a magnetic circuitincorporated in another embodiment of the present invention;

FIGS. 13 and 14 are perspective views showing actuators having magneticcircuits shown in FIGS. 6 and 9, respectively, which incorporate coils;

FIGS. 15 and 16 are exploded perspective and perspective views,respectively, showing a magnetic circuit incorporated in an actuatoraccording to still another embodiment of the present invention;

FIGS. 17A, 17B, and 17C are schematic views each showing a magneticfield distribution in the magnetic circuit shown in FIGS. 15 and 16;

FIG. 18 is a perspective view schematically showing an optical diskapparatus incorporating the magnetic circuit shown in FIGS. 15 and 16;

FIG. 19 is a perspective cutaway view schematically showing an actuatorand a magnetic circuit for producing a magnetic field which causes theactuator to move;

FIG. 20 is a perspective view showing the carriage shown in FIGS. 18 and19;

FIG. 21 is an exploded perspective view schematically showing a magneticcircuit shown in FIG. 19;

FIG. 22 is a sectional view taken along a line A--A of the optical diskapparatus shown in FIG. 18;

FIG. 23 is a sectional view showing a lens holder and associated partstaken along a line B--B of the optical disk apparatus shown in FIG. 18;

FIG. 24A is a partial sectional view showing a magnetic path of theactuator shown in FIG. 19;

FIG. 24B is a graph showing a magnetic flux distribution in a magneticcircuit shown in FIG. 24A;

FIGS. 25 and 26 are exploded perspective and perspective views showing amagnetic circuit incorporated in an actuator according to still anotherembodiment of the present invention;

FIGS. 27A, 27B, and 27C are schematic views each showing a magnetic fluxdistribution in the magnetic circuit shown in FIGS. 25 and 26;

FIG. 28 is a sectional view showing a part of an actuator incorporatingthe magnetic circuit shown in FIGS. 25 and 26;

FIG. 29 is a sectional view showing another part of the actuatorincorporating the magnetic circuit shown in FIGS. 25 and 26;

FIGS. 30, 31, and 32 are schematic views each for explaining aninfluence caused when a magnetic circuit of the present invention isapplied to an opto-magnetic recording apparatus;

FIG. 33 is a perspective view showing an upper structure of the carriageshown in FIG. 20;

FIG. 34 is a perspective view showing a lower structure of the carriageshown in FIG. 20;

FIG. 35 is an enlarged perspective view showing a part of the carriageshown in FIG. 20;

FIGS. 36A and 36B are sectional views showing a part of the lowerstructure of the carriage shown in FIG. 34;

FIGS. 37 and 38 are perspective views showing parts of the lowerstructure of the carriage shown in FIG. 34;

FIG. 39 is a sectional view showing a pin shown in FIG. 38

FIG. 40 is a plan view showing the carriage shown in FIG. 20;

FIGS. 41A and 41B are enlarged plan views showing a structure forsupporting the carriage shown in FIG. 20;

FIG. 42 is a plan view showing a rear structure of the optical diskapparatus shown in FIG. 18;

FIG. 43 is a perspective view partially showing a tracking coil and awiring structure for explaining an electrical connection at a stationaryside of the optical disk apparatus shown in FIG. 42;

FIG. 44 is a perspective view showing a carriage for explaining anelectrical connection between a focusing coil and a tracking coil shownin FIG. 42;

FIG. 45 is a view showing a shape of a plate-like wire member shown inFIG. 44A;

FIG. 46 is a perspective view showing the carriage shown in FIG. 20 andbalance weights attached thereto;

FIG. 47 is a perspective view showing the carriage shown in FIG. 20 anda detection portion for detecting a position of the carriage;

FIG. 48 is a perspective view showing a modification of a carriage nothaving a pin supporting leaf spring;

FIGS. 49, 50, and 51 are perspective and sectional views each showing amodification of a structure for bonding upper and lower structures of acarriage; and

FIG. 52 is a perspective view showing the carriage shown in FIG. 20.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 5 and 6 are exploded perspective and perspective views showing amagnetic circuit of an electro-magnetic actuator according to the firstembodiment of the present invention. Referring to FIGS. 5 and 6, amagnetic circuit 1 comprises two plate-like yokes 2 and 3 having thesame shape and size and two plate-like permanent magnets 4 and 5 havingthe same shape and size. The permanent magnets 4 and 5 are arranged tobe separated from each other so that the same poles of the permanentmagnets 4 and 5 are in contact with the same yoke. Opposing surfaces ofthe yokes 2 and 3 are formed flat, and the thicknesses of the permanentmagnets 4 and 5 in magnetization directions are equal to each other.Therefore, a distance between the opposite surfaces of the yokes 2 and3, i.e., a gap length is maintained constant along the oppositesurfaces. A space as a magnetic gap surrounded by the yokes 2 and 3 andthe permanent magnets 4 and 5 is a rectangular parallelpiped. In orderto obtain a long magnetic gap, the permanent magnets 4 and 5 arearranged on side end portions of the yokes 2 and 3, respectively.

In the magnetic circuit 1 shown in FIG. 6, magnetic fluxes generated bythe N poles of the permanent magnets 4 and 5 flow from the magnetic gapto the yoke 2 through the yoke 3 and return to the S poles of themagnets 4 and 5, thereby forming paths R1 as shown in FIG. 7. As shownin a front view of FIG. 7, in the magnetic circuit 1, flows of magneticfluxes which return through air around the magnetic circuit withoutpassing through the magnetic gap, i.e., magnetic paths R2 are generatedin addition to the magnetic paths R1. Magnetic fluxes flow in air by alonger distance in the magnetic paths R2 in which magnetic fluxesarcuately flow outside the magnetic circuit 1 than in the magnetic pathsR1 in which magnetic fluxes flow in the magnetic gap from the yoke 3 tothe yoke 2 by a shortest distance. Since a permeability of air is muchsmaller than that of the yoke 2 or 3, magnetic fluxes do not easily flowin air. Therefore, most of magnetic fluxes generated by the N polesreturn to the S poles through the magnetic paths R1. As described above,since the distance between the opposite surfaces of the yokes 2 and 3 isconstant along the surfaces, a distribution of magnetic fluxes in themagnetic gap is substantially constant along the surfaces.

A magnetic circuit obtained by decreasing the size of the magneticcircuit having the above arrangement will be described below incomparison with a magnetic circuit obtained by decreasing the size of aconventional magnetic circuit shown in FIG. 2. When the conventionalmagnetic circuit shown in FIG. 2 is made compact in size, the yoke 105causes magnetic saturation to prevent an easy flow of magnetic fluxes.Therefore, magnetic fluxes leak from a magnetic gap into air to change amagnetic flux density in the surface direction in the magnetic gap. Inthe magnetic circuit shown in FIG. 6, however, if the yoke 3 causesmagnetic saturation, magnetic fluxes exceeding saturated magnetic fluxesdo not flow into a portion of the yoke between hatched virtual sectionsshown in FIG. 8. The magnetic fluxes flow through magnetic paths R2x andR2y without passing though the sections. (Suffixes x and y indicate flowdirections of magnetic fluxes.) Therefore, magnetic fluxes passingthrough the magnetic gap do not change even in a magnetic saturationstate, and the magnetic flux density distribution is substantiallymaintained constant even if the magnetic circuit 1 is made compact insize. In the conventional magnetic circuit shown in FIG. 2, the yoke105, the permanent magnet 106, the magnetic gap, and the yoke 105b areso arranged as to be stacked with each other in a directionperpendicular to the magnetic gap. In the magnetic circuit shown in FIG.8, however, since the magnetic gap and the permanent magnets 4 and 5 arearranged in parallel with each other, the thickness of the magneticcircuit can be decreased. In addition, when an electro-magnetic actuator10 is constituted such that a coil 6 is inserted in a magnetic gap asshown in FIG. 13 or 14, the coil 6 can stably generate a driving forceat any position in the magnetic gap upon power supply and can smoothlymove in the magnetic gap. Therefore, when the coil 6 is connected to arecording/reproduction head of an optical disk apparatus or a magneticdisk apparatus, e.g., an objective lens or a magnetic head to drive thehead, information of interest can be accessed at a high speed by thehead.

FIG. 9 shows a magnetic circuit of an electro-magnetic actuatoraccording to the second embodiment o the present invention. In amagnetic circuit 11 shown in FIG. 9, a yoke 12 has a thickness twicethat of yokes 13a and 13b, and permanent magnets 14a and 15a andpermanent magnets 14b and 15b are arranged such that their magnetizationdirections are opposite to each other. That is, the magnetic circuit 11has a structure in which two magnetic circuits 1 shown in FIG. 8 arestacked in the magnetization direction. The magnetic circuit 11 formstwo magnetic gaps by the four permanent magnets 14a, 14b, 15a, and 15b.

In the magnetic circuit 11 having the above structure, a magnetic fluxdensity distribution in each of the two magnetic gaps is uniform alongthe opposite surfaces, and almost no change is produced in thedistribution even when the circuit is made small in size. In addition,in an electro-magnetic actuator 20 in which a coil 16 is wound to extendthrough the two magnetic gaps of the magnetic circuit 11 as shown inFIG. 14, the area of an effective winding portion of the coil 16 isincreased to be about twice that of an effective winding portion of themagnetic circuit shown in FIG. 13 to largely improve an operationefficiency of the coil, thereby increasing a driving force. Therefore,when the coil 16 is connected to a recording/reproduction head of anoptical disk apparatus or a magnetic disk apparatus, i.e., an objectivelens or a magnetic head to drive the head, information of interest canbe accessed at a higher speed with a higher precision.

FIG. 10 shows a magnetic circuit of an electro-magnetic actuatoraccording to the third embodiment of the present invention. A magneticcircuit 21 shown in FIG. 10 has a structure in which two magneticcircuits 1 shown in FIG. 6 are stacked in parallel with each other inthe magnetization direction. A permanent magnet 24 has a size twice thatof each of permanent magnets 25a and 25b, and two magnetic gaps formedby the permanent magnets 24, 25a, and 25b have the same shape.

The magnetic circuit 21 having the above structure can simultaneouslydrive two coils (not shown) by using the two magnetic gaps. The twocoils can be connected to a single movable member or different movablemembers. In the magnetic circuit 11 or 21 shown in FIG. 9 or 10,respectively, any number of magnetic circuits 1 can be arranged inseries or parallel with each other in the magnetization direction of thepermanent magnets. In addition, series and parallel arrangements can besimultaneously used. As shown in FIG. 11, for example, the magneticcircuits 21 shown in FIG. 10 may be connected to form a ring-likemagnetic circuit 31. In this case, a coil (not shown) is arranged ateach magnetic gap, and power is applied to these coils to obtain arotational driving force. The coils can be connected to a single movablemember or different movable members.

FIG. 12 shows a magnetic circuit of an electro-magnetic actuatoraccording to the fourth embodiment of the present invention. In amagnetic circuit 31 shown in FIG. 12, permanent magnets 34a, 34b, 35a,and 35b have different thicknesses from those of their magnetic gaps,and yokes 32 and 33a and yokes 32 and 33b slightly project in theirmagnetic gaps in the direction of thickness of the gaps. Distances(i.e., magnetic gaps) between opposite surfaces of projections 37a, 37b,37c, and 37d are constant along the surfaces. A small gap t2 is formedbetween each of the magnets 34a, 34b, 35a, and 35b and the magnetic gap.Assuming that the thickness of the magnetic gap is t1, the magneticcircuit is arranged to satisfy a relation of t1≦t2. Other arrangementsare the same as the magnetic circuit shown in FIG. 9.

In the magnetic circuit 31 having the above structure, the magnetic gapis narrowed by the projections even if the thicknesses of the permanentmagnets remain the same. Therefore, the thickness of the permanentmagnet can be increased relative to the magnetic gap to sufficientlyincrease a magnetic flux density in the magnetic gap. Similarly, adriving force of a coil (not shown) arranged in the magnetic gap can beimproved.

The projection portion need not be formed for each yoke as in themagnetic circuit 31 shown in FIG. 12. For example, the projections 37aand 37b may be formed for only the yokes 33a and 33b, and the yoke 32may be a normal flat plate.

FIGS. 15 and 16 show a magnetic circuit of an electro-magnetic actuatoraccording to the fifth embodiment of the present invention. A magneticcircuit 41 shown in FIGS. 15 and 16 has a stacking structure similar tothat of the magnetic circuit shown in FIG. 9, in which a groove isformed in a side portion of a yoke 43a having a larger thickness thanthat of a yoke 43b, and a plate-like permanent magnet 48 is arranged inthe groove. The surface of the S pole of the magnet 48 is fixed to theyoke 43a, and the surface of its N pole coincides with the side surfaceof the yoke 43a. Therefore, permanent magnets 44a, 44b, 45a, 45b, and 48are arranged such that the magnetization direction of the magnets 44a,44b, 45, and 45b becomes perpendicular to that of the magnet 48. Notethat the N and S poles of the permanent magnet 48 can be inverted.Although the length in the longitudinal direction and the thickness ofthe magnet 48 are slightly smaller than those of the groove of the yoke43a in this embodiment, they may be the same. In addition, although thewidth of the magnet 48 measured along the magnetized direction is setsuch that the N pole of the magnet 48 coincides with the side surface ofthe yoke 43a, it may slightly project from the side surface.

In the magnetic circuit 41 having the above structure, magnetic fluxdensity distributions as shown in FIGS. 17A to 17C are generated. FIG.17B shows a magnetic flux density distribution across the magnetic gap,and FIGS. 17A and 17C show a magnetic flux density distribution of themagnetization direction of the permanent magnet 48 along twoperpendicular lines. In the magnetic circuit 41, magnetic fluxesgenerated by the N pole of the permanent magnet 48 form a magnetic pathwhich passes through the yoke 43a and 42 and returns to the S pole ofthe magnet 48. Magnetic fluxes generated by the permanent magnet 48effectively flow inside the magnetic circuit 41 without disturbing aflow of magnetic fluxes in the magnetic circuit 41 generated by thepermanent magnets 44a, 44b, 45a, and 45b as in the magnetic circuit 1shown in FIG. 6. Therefore, a movable member can be driven in twodirections by using different flows of magnetic fluxes generated in themagnetic circuit 41.

An optical disk apparatus incorporating an electro-magnetic actuatorusing the magnetic circuit 41 shown in FIGS. 15 and 16 will be describedbelow with reference to FIGS. 18 to 24. FIG. 18 shows a perspectiveinner structure of the optical disk apparatus, FIG. 19 shows a movablemember and the magnetic circuit shown in FIG. 18, and FIG. 20 shows themovable member shown in FIGS. 18 and 19.

In order to optically read information from or optically writeinformation in an optical disk 61 shown in FIG. 18, an objective lens 62of an optical head is supported by a movable member 66 to oppose theoptical disk 61. An optical system is arranged such that a light beamgenerated by a light source such as a semiconductor laser provided in afixed optical system 74 outside the movable member 66 is guided to theobjective lens 62 through a beam splitter or a reflecting mirror. Thislight beam is focused on a track of the optical disk 61 by the objectivelens 62 to read information from or write information in the opticaldisk 61. The objective lens 62 is mounted on a lens holder 63, and oneend face of the holder 63 is elastically supported by two leaf springs64a and 64b. Therefore, the objective lens 62 is supported by the leafsprings 64a and 64b so that its optical axis coincides with the Zdirection.

A focusing coil 65 having the Z direction as its axis is wound aroundthe lens holder 63 so as to surround the objective lens 62 and forms afocusing electro-magnetic driving system together with magnetic circuits41-1 and 41-2 as shown in FIGS. 21 and 23. Note that the objective lens62, the lens holder 63, the focusing coil 65, and the like are mountedon the carriage 66 via the leaf spring 64a and 64b. The lens holder 63and the carriage 66 consist of a resin material such as plastic.

A tracking coil 67 wound around its axis along the X direction as shownin FIGS. 20 and 22 is fixed on the carriage 66, and guide rollermechanisms 68a and 68b are separately arranged along the Y direction andfixed at respective ends of the coil 67. The guide roller mechanism 68ahas a pair of guide rollers 70 elastically supported by leaf springs 69aand 69b, and the guide roller mechanism 68b has a pair of guide rollers71a and 71b fixed directly by the mechanism 68b. The guide rollers 70,71a, and 71b have rotating axes inclined by 45° with respect to the Ydirection and are in slidable contact with and roll along linear guides73a and 73b with a circular section fixed to a base 72 and having alongitudinal direction in the X direction. Therefore, the two ends ofthe carriage 66 are supported by the linear guides 73a and 73b so thatthe carriage 66 can move in the X direction. Note that the tracking coil67 forms a tracking electro-magnetic driving system together with themagnetic circuits 41-1 and 41-2.

The magnetic circuits 41-1 and 41-2 have basically the same structure asthat shown in FIGS. 15 and 16 except that the shapes of the yoke and thepermanent magnet are slightly different. Note that the magnetic circuits41-1 and 41-2 are symmetrically arranged about the center of gravity ofthe carriage 66.

The tracking coil 67 fixed to the carriage 66 is wound to be inserted infour magnetic gaps formed by the magnetic circuits 41-1 and 41-2, and issupported by the linear guides 73a and 73b so as to be kept in anon-contact state with respect to yokes 42-1, 42-2, 43a-1, 43a-2, 43b-1,and 43b-2. In the actuator shown in FIGS. 18 and 19, the focusing coil65 and permanent magnets 48-1 and 48-2 oppose each other via a gap. Thelength of each of the magnets 48-1 and 48-2 is sufficient to allow themagnet to oppose the carriage 66 throughout the entire movable distance.

An operation of the optical disk apparatus having the arrangement shownin FIG. 18 will be described below. In order to drive the objective lens62 in the X direction, a current is flowed through the tracking coil 67.A Lorentz force, i.e., a driving force is generated in the X directionby a direction (Y direction) of the current and a direction (Zdirection) of magnetic fluxes in magnetic gap of the magnetic circuit41-1 and 41-2. Since a magnetic flux density in the magnetic gap isconstant, a driving amount, a driving direction, and a driving speed aredetermined by controlling the current to be supplied to the trackingcoil 67. The carriage 66 moves along the linear guides 73a and 73belongated in the X direction while the guide rollers 70, 71a, and 71broll on the linear guides in accordance with a driving force applied tothe tracking coil 67. The objective lens 62 is roughly moved to apredetermined position in the radial direction of the optical disk 61and then finely positioned thereat.

In order to drive the objective lens 62 in the Z direction, a current isflowed through the focusing coil 65, and a driving force is generated inthe Z direction by a direction (X direction) of the current and adirection (Y direction) of magnetic fluxes of the permanent magnets 48-1and 48-2. A driving amount, a driving direction, and a driving speed aresimilarly determined by controlling the current to be supplied to thefocusing coil 65. The lens holder 63 is moved while equally curving thetwo leaf springs 64a and 64b in accordance with a driving force appliedto the focusing coil 65. A spot of a light beam formed by the objectivelens 62 is finely positioned at a predetermined position on the opticaldisk 61 and correctly focused thereon.

The current to be supplied to the focusing coil 65 is supplied via theleaf springs 64a and 64b, and terminals (to be described in detaillater) provided at the other ends of the springs 64a and 64b andprojecting from the carriage 66 are connected to a power source.

In the above optical disk apparatus, since a magnetic flux densitydistribution in the magnetic gap is uniform along the inner surface ofthe yoke upon driving of the objective lens 62 in the X direction, aconstant driving force can be obtained in the magnetic gap. In aconventional magnetic circuit, a magnetic flux density is largelydecreased at both ends of the magnetic gap. In the magnetic circuits41-1 and 41-2 shown in FIGS. 18 and 19, however, a magnetic flux densityis not largely decreased even at both ends of the magnetic gap, and astable driving force can be obtained at the central portion or both theend portions of the magnetic gap. Therefore, power supply control withrespect to the tracking coil 67 need not be changed regardless of theposition of the carriage 66, resulting in very simple control. Inaddition, even if the magnetic circuits 41-1 and 41-2 are made compactin size as a whole or a magnetomotive force of the permanent magnet isincreased to exceed a saturated magnetic flux density of the yoke, amagnetic flux density to be applied to the tracking coil 67 issubstantially uniform along the inner surface of the magnetic gap.Therefore, a substantially constant driving force is generatedregardless of the position of the carriage 66.

The permanent magnet 48 provided to apply a magnetic force to thefocusing coil 65 applies magnetic fluxes to also the tracking coil 67.If the magnet 48 is mounted in the same direction as that of a flow ofmagnetic fluxes in the magnetic gap as shown in FIG. 24B, a magneticflux density distribution as indicated by a curve I in FIG. 24B isobtained to allow the driving force to be generated at a portion nearthe center of the carriage 66. Therefore, in a structure in which theweight of the entire carriage 66 is relatively concentrated in a portionnear its center, the magnetic flux density distribution indicated by thecurve I is preferred. When the magnetization direction of the permanentmagnet 48 is fixed to be opposite to that shown in FIG. 24A, a magneticflux density distribution in the magnetic gap is increased to be amagnetic flux density distribution as indicated by a curve II in FIG.24B. Therefore, in a structure in which the weight of the entirecarriage 66 is relatively concentrated in a portion near its terminalend portion, i.e., a portion near the guide rollers 73a and 73b, themagnetic flux density distribution indicated by the curve II ispreferred.

FIGS. 25 and 26 show a magnetic circuit of an electro-magnetic actuatoraccording to the sixth embodiment of the present invention. In amagnetic circuit 51 shown in FIGS. 25 and 26, instead of the permanentmagnet 48 shown in FIGS. 15 and 16, a permanent magnet 58 is arranged ina groove of a yoke 52 and fixed to the yoke 52. The length in thelongitudinal direction of the magnet 58 is slightly smaller than thelength of the groove of the yoke 52, and the thickness of the magnet 58is set equal to the thickness of the yoke 52. However, the dimensionsare not limited to those in this embodiment.

In the magnetic circuit 51 having the above structure, magnetic fluxdensity distributions shown in FIGS. 27A, 27B, and 27C are generated.FIG. 27B shows a magnetic flux density distribution of a magnetic gapalong the magnetic gap, and FIGS. 27A and 27C show a magnetic fluxdensity distribution along the magnetization direction of the permanentmagnet 58 and a magnetic flux density distribution along a directionperpendicular to the magnetization direction.

In the magnetic circuit shown in FIGS. 25 and 26, since magnetic fluxesgenerated by the N pole of the permanent magnetic 58 return to upper andlower yokes 53a and 53b, a reluctance can be reduced in comparison witha magnetic path passing through a space around the magnetic circuit. Asa result, a magnetic flux density on the end face of the magnetic posecan be further increased.

When the electro-magnetic actuator including the above magnetic circuit51 is to be incorporated in an optical disk apparatus, the magneticcircuit 51, the carriage 66 and the lens holder 63 are arranged as shownin FIGS. 28 and 29. FIG. 28 shows the same portion as in the sectionalview of the actuator taken along the line B--B in the above embodimentshown in FIG. 23, and FIG. 29 is a sectional view of the actuator in anXZ plane including the center of the carriage 66. In order toeffectively use magnetic fluxes generated by permanent magnets 58-1 and58-2, two pairs of four flat focusing coils 65a-1, 65a-2, 65b-1, and65b-2 wound to have the Y direction as their axes are fixed to sidesurface of the lens holder 63 in positions at the carriage 66 sideopposing the magnets 58-1 and 58-2. Two leaf springs 64a and 64b arearranged to sandwich a tracking coil 67 with an equal distance therefromand elastically support a lens holder 63. Other arrangements are thesame as those of the optical disk apparatus as described above. In thisembodiment, since a magnetic flux density distribution in a magnetic gapis uniform along the inner surface of the yoke upon driving of anobjective lens 62 in the X direction, a constant driving force can beobtained in the magnetic gap.

In the magnetic circuit shown in FIGS. 25 and 26, by fixing the magneticpole of the permanent magnet 58 in an opposite direction as shown inFIG. 24A, the magnitude of a magnetic force to be applied to thetracking coil 67 can be changed.

In the fifth and sixth embodiments, a flow or distribution of magneticfluxes can be adjusted by providing an additional permanent magnet tothe magnetic circuits 41 and 51. In addition, the same effect can beobtained by providing an additional permanent magnet to the magneticcircuits 1, 11, 21, and 31 according to the first to fourth embodiments.Although a description is omitted, the magnetic circuits 1, 11, 21, and31 of the first to fourth embodiments can be used to drive an opticalhead or the like.

An influence of a magnetic field caused by the magnetic circuit of thepresent invention on an optical disk will be described below withreference to FIGS. 30 to 32. As shown in FIG. 30, in an opto-magneticrecording/reproduction apparatus, an auxiliary magnetic field generatingdevice 81a is provided to oppose the magnetic circuit via anopto-magnetic disk 61 and applies a magnetic field to the disk 61. Ingeneral, in order to perform both recording and reproduction ofinformation in an opto-magnetic recording/reproduction apparatus, theintensity of a light beam to be radiated onto an optical disk must bemaintained constant to keep a magnetic moment in one direction on arecording surface of the opto-magnetic disk. For this purpose, a biasmagnetic field must be applied to the surface of the opto-magnetic disk.In order to maintain the magnetic moment constant, opposite biasmagnetic fields must be used in recording and reproduction ofinformation. An auxiliary magnetic field generating device 81a as anelectromagnet is provided to invert the magnetic poles. The device 81ahas a yoke 82a and a coil 83a and forms a flow of magnetic fluxes asindicated by an arrow in FIG. 30, thereby recording information. Thedevice 81a reverses the direction of a current to be supplied to thecoil 83a to form a flow of magnetic fluxes opposite to that shown inFIG. 30, thereby reproducing information.

In the above arrangement the magnetic flux flow from the permanentmagnet 48 reaches the surface of the opto-magnetic disk 61 to supply amagnetic field in the Z direction. Therefore, magnetic fluxes of thepermanent magnet 48 contribute to (1) focusing coil driving, (2),tracking coil driving, and (3) magnetic field supply to the surface ofthe opto-magnetic disk. By the effect of item (3), a magnetic force(i.e., an amount of a current to be supplied to the coil 83) generatedby the auxiliary magnetic field generating device 81a can be suppressed.

FIG. 31 is a sectional view showing an influence of a magnetic field onan opto-magnetic disk obtained when the magnetic circuit 51 is used.Note that other arrangements are the same as shown in FIGS. 28 and 29.In this embodiment, most of magnetic fluxes from the permanent magnet 58are absorbed by yokes 53a and 53b, and almost no magnetic fluxes reachthe surface of an opto-magnetic disk 61. Therefore, when recording,reproduction, and erasure of information is realized by modulation of anauxiliary magnetic field intensity on the recording surface of the disk61, an operation is not influenced by the magnetic circuit for drivingan actuator. As a result, a bias magnetic field corresponding to acurrent amount to be flowed to the coil 83b of the auxiliary magneticfield generating device 81b can be generated.

As shown in FIG. 32, magnetic fluxes generated by the device 81a form aneffective magnetic path flowing through the yoke 53a of the magneticcircuit 51. For this reason, an amount of magnetic fluxes which flow onthe recording surface of the opto-magnetic disk 61 and return to theyoke 81b after passing through the yoke 53a is increased. Therefore, apassing magnetic flux density on the recording surface of the disk 61with respect to the current amount to be supplied to the coil 83b isfurther increased to suppress an amount of unnecessary magnetic fluxeswhich leak into air.

When the direction of a current to be supplied to the coil 83b isreversed, magnetic fluxes generated by the auxiliary magnetic fieldgenerating device 81a and passing through the yokes 53a-1 and 53a-2 varymagnetic fluxes for driving the focusing coils 65a-1 and 65a-2. Ingeneral, however, an amount of magnetic fluxes generated by the device81a is smaller than that of magnetic fluxes generated by the magneticcircuit 51. That is, an amount of magnetic fluxes to be supplied to therecording surface of an opto-magnetic disk is smaller than that ofmagnetic fluxes for focus driving. For this reason, when the directionof magnetic fluxes of the auxiliary magnetic field generating device 81ais reversed with respect a magnetic flux density distribution curve asindicated by a solid line in FIG. 32, a magnetic flux densitydistribution only slightly changes as indicated by a broken line, and adriving force does not change much. Therefore, even if the direction ofmagnetic fluxes is reversed, almost no variation is caused in magneticfluxes in a magnetic flux density distribution to be given to thefocusing coils 65a-1 and 65a-2, and a stable driving force is constantlysupplied to the coils 65a-1 and 65a-2.

The structure and parts of the optical disk apparatus shown in FIG. 18will be described in more detail below with reference to FIGS. 33 to 53.

The movable member shown in FIG. 20, i.e., the carriage 66 isconstituted by an upper structure shown in FIG. 33 and a lower structure8 shown in FIG. 34. As described above, the upper structure 7 has afunction as a focus actuator for moving an objective lens 62 along itsoptical axis. The upper structure 7 comprises a lens holder 63, afocusing coil 65 wound to have the Z direction as its axis, two parallelleaf springs 64a and 64b for elastically supporting the lens holder 63,and a focus actuator fixing section 17 for fixing the other ends of thesprings 64a and 64b.

The lens holder 63 is formed by molding, e.g., injection molding from aresin material and has a ring-like snap 18 for fixing the objective lens62 by fastening as shown in FIG. 33. The snap 18 may be moldedintegrally with or independently from the lens holder 63. Alternatively,a flange portion of the objective lens 62 may be adhered and fixed tothe lens holder 63 without using the snap 18. The focus actuator fixingsection 17 is formed by molding from a resin material to have attachmentholes 19a to be connected to the lower structure 8 (to be describedlater).

The parallel leaf springs 64a and 64b for connecting the lens holder 63and the focus actuator fixing section 17 consist of a conductivematerial. Terminal end portions of the springs 64a and 64b are fixed tothe focus actuator fixing section 17 and the lens holder 63, and theirend portions 19b and 19c are exposed from the fixing section 17 in orderto supply a current to the focusing coil 65. That is, the parallel leafsprings 64a and 64b also serve as power supply members for supplying acurrent to the focusing coil 65. Wirings of the focusing coil 65 and thetracking coil 67 will be described in detail later.

FIG. 34 shows the lower structure 8 of the optical head apparatus. Inthe structure 8, the tracking coil 67 is fixed integrally with acarriage molded by using a resin material and constituted by carriagesections 26a, 26b, and 26c. The guide rollers 70, 71a, and 71b such asthree pairs of six bearings are provided on both side surfaces of thelower structure 8. Note that although the tracking coil 67 is molded asa single coil connecting the carriage sections 26b and 26c in thisembodiment, different coils may be provided between the carriagesections 26a and 26b and between the carriage sections 26b and 26c.Alternatively, as shown in FIG. 33, a resin part for reinforcing thetracking coil 67 for connecting the section 26a to the sections 26b and26c may be provided to the coil 67 so that the section 26a is notconnected to the sections 26b and 26c by only the coil 67. In addition,the number of bearings is not limited to three pairs of six bearings asshown in FIG. 20.

The central carriage section 26a for increasing the rigidity of thetracking coil 67 is molded to be hollow, and a light beam passes throughinside the section 26a. That is, a guiding optical system and adetecting optical system at a fixed side are optically connected to adisk via a reflecting mirror 29 fixed to the carriage 66 below theobjective lens 62. Attachment pins 27 to be fitted in the attachmentholes 19a of the focus actuator fixing section 17 are formed integrallywith the upper surface of the central carriage section 26a. The section26a and the attachment portion of the section 17 are shown in detail inFIG. 35. As shown in FIG. 35, when each pin 27 is inserted in acorresponding one of the holes 19a, a predetermined gap is formedbetween the two members. In addition, a small amount of adhesive 28 ispresent between bonding surfaces of the section 26a and 17. According tosuch an attaching method, inclination adjustment for setting the opticalaxis of the objective lens 62 to be perpendicular to the disk surfacecan be easily performed. That is, upon attachment of the carriage 66 andthe focus actuator fixing section 17, the inclination of the lens 62 canbe adjusted by the section 17 which can be easily operated, resulting inthe following advantage.

It is difficult to adjust the inclination of the objective lens 62 whenthe lens 62 is to be fixed to the lens holder 63 since a space betweenthe objective lens 62 and the lens holder 63 is narrow. Therefore, easyadjustment of the inclination of the lens 6 performed by using the focusactuator fixing section 17 contributes to an improvement in productivityof the optical head apparatus. The inclination of the reflecting mirror29 can also be easily adjusted. FIG. 36A shows a positional relationshipbetween the carriage 66 and the mirror 29, and FIG. 36B shows aconnecting portion between the two members. The triangular-prismreflecting mirror 29 is fixed to a mirror attachment surface of thecentral carriage section 26a via the adhesive 38. If the reflectingmirror 29 is directly adhered on the mirror attachment surface withoutperforming positional adjustment, the mirror 29 cannot be fixed with apredetermined inclination with respect to the optical axis due tovariations in assembly precision of the carriage 66 or parts precisionthereof or the like. Therefore, the adhesive 38 is interposed in anattachment gap and the inclination of the mirror 29 is adjusted in apredetermined direction before the adhesive 38 is hardened, therebyfacilitating inclination adjustment. As a result, stable opticalcharacteristics of the reflecting mirror 29 are realized. In order toadjust the predetermined position and inclination of the mirror 29, anyof rectangular surfaces except for a reflecting surface 29a and anadhesion surface 29b and triangular surfaces of the triangular prism,e.g., a rectangular surface 29c in this embodiment shown in FIG. 36B isa non-adhesion surface serving as a chucking surface for holding themirror 29 upon adhesion. Although not shown, the reflecting mirror 29may be connected to another member in advance and this member may beadhered to the carriage 66 so that the reflecting surface is adjusted tohave a predetermined inclination.

The two side carriage sections 26b and 26c will be described below withreference to FIGS. 37 and 38. Two pairs of four pins 39 for attachingthe two pairs of four guide rollers 70, 71a, and 71b by adhesion orfitting are molded integrally with the side carriage section 26b. Theaxial directions of the upper and lower pairs of pins 39 aresubstantially perpendicular to each other, and the pins 39 arepositioned beforehand upon molding such that the rotating shafts of theguide rollers 70, 71a, and 71b are set to be substantially perpendicularto the direction of the linear guides. This positioning is similarlyperformed for the other pins 39 by using a suitable jig upon molding ofthe section 26b.

The inclination of the carriage 66 with respect to the linear guides 73aand 73b is determined by a contact state of the guide rollers 70, 71a,and 71b with respect to the linear guides 73a and 73b. Therefore, amolding material is injected to fix the pins 39 which are positionedwith respect to metal molds, thereby improving position accuracy betweena plurality of pins and inclination accuracy of the carriage 66.Similarly, a relative position between the tracking coil 67 and the pins39 can be determined by injecting a molding material to fix the trackingcoil 67 which are positioned with respect to metal molds. Satisfactoryprecision in assembly of the carriage can be assured by keeping theprecision of the metal molds.

As shown in FIGS. 37 and 38, the side carriage section 26c isconstituted by a fixed part 59a to which the tracking coil 67 is fixedand a deformation part 59b, fixed on the fixed part 59a, for absorbing areaction force applied on the guide rollers 71a and 71b when the rollers71a and 71b are placed on the linear guides 73a and 73b. That is, inthis deformation part 59, the two guide rollers 70, 71a, and 71b areelastically supported at their two ends by the leaf springs 69a and 69bto form a symmetrical beam structure. Therefore, when the guide rollers70, 71a, and 71b receive a reaction force from the linear guides 73a and73b, the pins 39 are displaced in the Y direction without beinginclined. The outer side surface of the fixed part 59a is formed to havea U-shaped section, and its upper and lower projections form positioningguides 47a and 47b. Positioning pins 47f are formed integrally with thecarriage section 26c between the upper and lower positioning guides 47aand 47b. In the deformation part 59b, the guide roller attachment pins39 and the leaf springs 69a and 69b are fixed to a base segment 74a.That is, in a molding step, a pair of two pins 39 for attaching a pairof two guide rollers 70, 71a, and 71b are positioned to be perpendicularto each other and embedded integrally with the leaf springs 69a and 69bin the deformation part 59b. The springs 69a and 69b are fixed toattachment segments 74b and 74c to be fitted in a recess between thepositioning guides 47a and 47b, and the pins 47f are inserted inattachment holes 75a of the segments 74b and 74c to fix the deformationpart 59 b to the fixed part 59a. Note that the leaf springs 69a and 69bneed not take a two-end-supported beam structure but may take acantilever structure. Alternatively, instead of forming the springs 69aand 69b by a single plate, a pair of two parallel springs 69a and 69bmay be used to allow the pins 39 to be displaced.

FIG. 39 shows a practical arrangement of the guide roller attachment pin39. The pin 39 shown in FIG. 39 consists of a material different fromthe resin material of the side carriage sections 26b and 26c to whichthe pin is attached. A return portion 39a is formed at a portion to beembedded of the pin 39 so as to improve bite of a molding material uponmolding, and positioning contact portions 39b and 39d are formed atupper and lower end portions thereof. A positioning flange portion 39cto be brought into contact with the guide rollers 70, 71a, and 71b isformed around the pin 39. The contact portion 39d fixes and supports thepin 39 by using a jig upon molding of a member to which the pin isattached. Note that the pin 39 shown in FIG. 39 is only an example andthe present invention is not limited to this. For example, the pin 39may be formed of the same material as that of a member to which the pinis attached. In this case, by forming a hole corresponding to the shapeof the pin 39 in a metal mold for molding the pin attachment member, theprojecting pin 39 can be molded integrally with the pin attachmentmember.

FIGS. 40, 41A and 41B show a planar positional relationship between thecarriage 66 and linear guide 73a and 73b. In this arrangement, when thecarriage 66 is driven in the X direction by an interaction between themagnetic circuits 41-1 and 41-2 and the coil 67, an advantage of elasticsupport of the guide rollers 70, 71a, and 71b by the leaf springs 69aand 69b is effectively achieved. This advantage will be described withreference to FIG. 41A. Note that a virtual line denoted by referencenumeral 75 in FIG. 41A indicates an outline of the springs 69a and 69bwhich are elastically returned. Upon X-direction driving, the guiderollers PG,51 70, 71a, and 71b at the carriage section 26c side areurged against the linear guide 73b by an elastic force of the springs69a and 69b. At this time, a force F0 applied from the linear guide 73bonto the guide rollers 70, 71a, and 71b is absorbed in the carriage 66due to flexure of the springs 69a and 69b. Therefore, an unnecessaryvibration of the carriage 66 caused by a specific play of each of theguide rollers 70, 71a, and 71b can be suppressed. When the two guiderollers are supported by the two-end-supported beam structure as shownin FIG. 40, the rotating shafts of the two guide rollers 70, 71a, and71b are kept perpendicular to the linear guide direction even if thesprings 69a and 69b flex. Therefore, a frictional resistance of theguide rollers 70, 71a, and 71b can be reduced when the linear motorcarriage 66 is driven.

In addition, as shown in FIG. 41B, when a vibration damping materialsuch as rubber or a gel material is interposed between the leaf springs69a and 69b and the side carriage section 26c to add a vibration dampingelement in parallel with the springs 69a and 69b, a vibration caused bydisplacement produced between the springs 69a and 69b and the carriagesection 26c can be reduced by a vibration damping member 76. That is, anunnecessary vibration produced upon driving of the carriage 66 can bereduced.

In the optical disk apparatus shown in FIG. 19, a light beam emittedfrom a light source located in the fixed optical system 74 fixed to thebase 72 is transmitted through a guiding optical system including ashaping prism, a collimator lens, and the like located in a fixedoptical system 94 similar to the light source, incident in the openingof the central carriage section 26a, and guided onto the surface of thedisk 61 through the reflecting mirror 29 and the objective lens 62. Thedisk 61 is loaded via a spindle motor (not shown) mounted on the base72. The light beam reflected and modulated by the surface of the disk 61is transmitted through the objective lens 62 and the reflecting mirror29 and guided to a detecting optical system located in a fixed opticalsystem 76 and including a focusing lens, a photodetector, and the like.Therefore, the light beam is radiated onto the disk upon driving of theobjective lens 62 in the Z and X directions to realize reproduction andrecording of information with respect to the disk.

As described above, by fixing each member integrally with the integrallymolded movable member, an optical head apparatus which is light inweight and causes no unnecessary vibration can be realized withoutcomplexity in manufacture/assembly. Especially when the presentinvention is applied to a separate type optical head as in thisembodiment, positioning and inclination precision of the tracking coil67 can be improved by the above structure. Therefore, no-contactinsertion of the tracking coil 67 can be easily performed even when themagnetic gaps of the magnetic circuits 41-1 and 41-2 are formed to becomparatively narrow. In other words, response characteristics ofX-direction driving of the carriage 66 can be improved. In addition,since the three carriage sections 26a, 26b, and 26c are connected by thetracking coil 67, a coil bobbin or another coil attachment sectionrequired by a conventional separate head apparatus need not be used.Furthermore, since the tracking coil 67 is used as a structural member,the optical head apparatus can be effectively made light in weight.

A wiring structure of the optical head apparatus according to the aboveembodiment will be described below. FIG. 42 shows a rear surface side ofthe optical head apparatus shown in FIG. 18. As shown in FIG. 42, aflexible print wire 77 for supplying power to the focusing coil 65 andthe tracking coil 67 is arranged symmetrically about the X direction.That is, this print wire 77 is arranged with a predetermined curvaturebetween a wire terminal 77a at the fixed side and a wire terminal 77b atthe movable side. The fixed-side siring terminal 77a is fixed alongsurfaces 78a parallel to the direction of the linear guides formed onthe base 72 and is connected to a power source (not shown). Themovable-side wire terminal 77b is fixed along side surfaces 78b parallelto the surfaces 78a of the side carriage sections 26a and 26b.

In the above wiring structure, even when the carriage 66 is moved in theradial direction of the disk, since the curvature of the print wire 77is maintained constant, no unnecessary counterforce is produced from theprint wire 77 to the carriage 66. Therefore, the carriage 66 can bestably moved regardless of inner and outer portions of the disk.

FIG. 43 shows a connection structure between the print wire 77 and thetracking coil 67. A conductive lead wire 79 of the tracking coil 67 isformed inside the side carriage section 26c upon molding of the section26c, and a portion 79a of the wire 79 is exposed at a lower portion ofthe carriage section 26c. The exposed portion 79a of the lead wire 79 issoldered to the movable-side flexible wire terminal 77b. In order toguide the lead wire 79 to the flexible wire 77, the number of turns ofthe tracking coil 67 is an even number. If, however, the number of is anodd number, the lead wire 79 is extended to the movable-side terminal77b. The above arrangement of the lead wire 79 is similarly formed inthe other side carriage section 26b.

FIG. 44 shows a connection structure for supplying a current to thefocusing coil 65. The two movable-side terminals 77b connected to thefixed-side terminal 77a via the flexible wire 77 are also connected toexposed portions 74a of focus wires 74 at the carriage sections 26b and26c. The focus wires 74 are plate- or rod-like conductive membersembedded in the carriage sections 26a, 26b, and 26c constituting thecarriage section upon molding of these sections and extended to thecentral carriage section 26a through behind the tracking coil 67.Exposed portions 74b of the wires 74 at the section 26a side aresoldered to lead wires 76, and the other ends of the lead wires 76 aresoldered to end portions 19b and 19c of the leaf spring 64a exposed atthe focus actuator fixed section 17 side. Lead wires 78 of the focusingcoil 65 are soldered to terminals 19e and 19f of the leaf spring 64bexposed at the lens holder 63 side. Since the leaf springs 64a and 64bare electrically connected via the parallel leaf springs 64 also servingas power supply members, they can be energized by supplying a currentfrom the power source to the focusing coil 65.

FIG. 45 shows a practical shape of the plate-like focus wires 74separated from the carriage 66. Referring to FIG. 45, the exposedportions 74a at the side carriage sections 26b and 26c side arepositioned in an opposite direction to that shown in FIG. 44. However,the exposed position can be arbitrarily selected, and the positions orthe like of the lead wire 79 or the movable-side terminals 77b can bearbitrarily changed in accordance with the exposed position. As shown inFIGS. 42 to 45, by molding a lead wire 79 or the focus wire 84integrally with the carriage 66, complexity in the shape of the flexiblewire can be eliminated.

Other embodiments of the present invention will be described below withreference to FIGS. 46 and 47.

In the embodiment shown in FIG. 46, balance weights are attached to acarriage 66. In order to drive the carriage 66 in the radial directionof a disk, a driving force must be applied on the center of gravity ofthe carriage so as not to produce an unnecessary vibration. In theembodiment shown in FIG. 46, therefore, balance weights 84 and 85 areattached to the carriage 66. These balance weights 84 and 85 arearranged at upper and lower portions or right and left portions of thecarriage. A shown in FIG. 46, by fitting attachment holes 84a onattachment pins 86a of carriage sections 26b and 26c, the balanceweights are fixed by adhesion to the carriage sections 26b and 26c ofthe carriage 66. Alternatively, the balance weights are fixed integrallywith the carriage sections 26b and 26c upon molding of the resinportions of the carriage 66.

In the embodiment shown in FIG. 47, a carriage 66 includes a portion 87to be detected for detecting the position of the carriage 66 moved inthe radial direction of a disk. The portion 87 is fixed integrally witha carriage section 26b of the carriage 66 or fixed by adhesion to thecarriage section 26b. When a position detecting unit 88 arranged in thefixed part detects the portion 87 to be detected, a position of thecarriage 66 in the disk radial direction is detected.

FIG. 48 shows a modification of the system of supporting the guiderollers 70, 71a, and 71b at the carriage section 26c side. In thismodification, the leaf springs 69a and 69b are omitted, and the basesegment 74a and the guide roller attachment pins 39 are formedintegrally with the section 26c. In this case, although the guiderollers 70, 71a, and 71b are not elastically supported by the leafsprings 69a and 69b, a play in each of the guide rollers 70, 71a, and71b can be removed by additionally providing a structure for supportingthe linear guide 73b in the Y direction to allow a small dislocation ofthe guide 73b.

FIGS. 49 and 50 show a modification of the attachment structure betweenthe focus actuator 65 and the carriage 66. As shown in FIG. 49, theupper surface of the carriage section 26a and the lower surface of thefocus actuator fixing section 17 are formed to have a recess 90 and aprojection 92, respectively. The recess 90 and the projection 92 areengaged with each other to improve the connection strength. The gap,i.e., the adhesive layer is formed in the connecting portion between thefocus actuator 65 and the carriage section 26a. Therefore since thebonding force of the adhesive layer is unsatisfactory with respect toX-direction driving of the carriage 66, the position of the focusactuator 65 may be deviated relative to the carriage section 26a. Inorder to prevent this positional deviation, as shown in FIG. 50, athrough hole 98 is formed in the focus actuator 65, and a reinforcingmember 96 is projected at the height of the center of gravity in the Zdirection of the focus actuator 65 from the carriage section 26a sideand fixed to the focus actuator fixing section 17. Since the connectingsurface between the reinforcing member 96 and the actuator fixingsection 17 is set in the Z direction, i.e., a direction perpendicular tothe X direction as the radial direction, no positional deviation isproduced between the upper and lower structures 7 and 8 when thecarriage 66 is transported, thereby improving tracking properties of theobjective lens 6 with respect to X-direction driving of the carriage 66.

FIG. 51 shows a connecting portion between the focus actuator 65 and thecentral carriage section 26a of the carriage 66 according to amodification of the carriage structure. In this structure, the twomembers including an adjustment margin are bonded by an adhesion portion93.

FIG. 52 is an exploded view showing the focus actuator 65, the carriage66, and their additional members shown in FIGS. 18 to 20, 13, and 35. Adetailed arrangement of each additional member is as described above.The balance weight 84 is molded integrally with a resin, and a positiondetecting slit 87 is positionally adjusted and adhered to the carriage66.

In order to apply the present invention to a standard optical headapparatus such as a conventional optical head apparatus 100, a chassis103 of the standard optical head apparatus 100 is molded, and a trackingcoil 108, guide roller support pins, and the like are molded integrallywith the chassis 103. Thereafter, optical parts such as an opticalpickup 104, a semiconductor laser, a collimator lens, and aphotodetector, or an optical head in which these parts are integratedare or is connected to the chassis 102, thereby constituting an opticalhead actuator. In this case, a problem of a heavy weight of aconventional apparatus is solved, and a compact and light standardoptical head which can move at a high speed and has an improved assemblyprecision is obtained.

In each of the above embodiments, a resin material is used as a moldingmaterial. However, the same effects as in the above embodiments can beobtained by using a ceramic, an aluminum alloy, a magnesium alloy, orthe like instead of the resin material. Note that insulation withrespect to the wiring system must be considered when an alloy materialis used.

Although an optical disk apparatus is taken as a example of an opticalrecording/reproduction apparatus in each of the above embodiments, thepresent invention is not limited to these embodiments. In addition, anoptical recording/reproduction apparatus using an opto-magnetic disk, anoptical card, an opto-magnetic card, or the like as an optical recordingmedium may be used. Furthermore, the present invention can be appliednot only to a linear type apparatus as in the above embodiments but alsoto a rotary type apparatus.

As has been described above, according to the present invention, thereare provided an electro-magnetic actuator which can constantly provide astable driving force and can be made compact in size and an optical diskapparatus which can reliably perform positioning control.

According to an optical head of the present invention, a movable memberis integrally molded by using a resin material (or a material such as aceramic, an aluminum alloy, or a magnesium alloy) which is comparativelylight in weight. Therefore, an optical head which has improved vibrationcharacteristics, is compact in size and light in weight, has highproductivity, and can move at a high speed can be provided. Therefore,problems of both of conventional separate type and standard opticalheads can be solved.

Since the optical head actuator has the structure wherein the separatedsections are coupled, the movable members and molding metal molds can beeasily manufactured. In addition, since an adhesive is flowed andhardened in a gap of a connecting portion between the upper and lowermovable members (structures), an inclination of an objective lens can beeasily adjusted. This adhesion scheme using a gap and an adhesive isalso effective in inclination adjustment for a reflecting mirror. Byusing a means for engaging not only the connecting portion of the upperand lower movable members but also connecting portions of other members,these members can be easily and tightly connected. As a result, theproductivity can be further improved.

When guide roller support pins at one side surface are arranged to besupported via elastic support members, an unnecessary rotationalvibration caused by a play in each guide roller rolling on a fixed guideshaft can be suppressed. If vibration damping elements are additionallyprovided in parallel with the elastic support members, an unnecessaryvibration can be further effectively suppressed.

Since the guide roller support pins of this type can be molded togetherwith the movable member by using the same type of material as themolding material, pins having improved inclination or positionalprecision can be obtained. Even when the pins are formed by using amaterial different from the molding material, the inclination orpositional precision of the pins or an attachment precision of the guiderollers can be further improved by forming a return portion, contactportions, a flange, and the like.

Since a flexible wire which can track driving of the movable member isused as a wire, arranged between a current supply side and a movablemember side, for supplying power to a coil, difficulty of supplying acurrent to a moving movable member is eliminated.

A lead wire of a tracking coil is exposed at the movable member side ofthe print wire through inside the resin material of the movable member,and the shape of the lead wire is improved. As a result, the print wireand the tracking coil can be easily electrically connected. In addition,since a wire member for a focusing coil (or another lens driving means)is embedded beforehand in a carriage section of the movable portion, thefocusing coil can be easily electrically connected to the print wire.

In a standard optical head, a wire for supplying power to an opticalhead can be guided to a movable portion by the same method.

The optical head apparatus according to the present invention caninclude members as used in a conventional optical head such as anobjective lens attachment portion, a portion to be detected fordetecting a position of the movable member, and balance weights. In thiscase, these members can be molded integrally with the movable member toreduce the number of attachment operations.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details shown and described. Accordingly,various modifications may be made without departing from the spirit orscope of the general inventive concept as defined by the appended claimsand their equivalents.

What is claimed is:
 1. An apparatus for generating a driving force,comprising:a first yoke, having a flat surface, for allowing magneticfluxes to pass therethrough; a second yoke, having one and opposite flatsurfaces, said one surface opposing one surface of said first yoke via afirst gap, and arranged in a first direction, for allowing magneticfluxes to pass therethrough; a third yoke, having one flat surfaceopposing the opposite surface of said second yoke via a second gap, andarranged in the first direction, for allowing magnetic fluxes to passtherethrough; first and second plate-like permanent magnets each havingsurfaces of one and another poles, separately arranged in said first gapin a second direction perpendicular to the first direction, the surfaceof the one pole being fixed to the surface of said first yoke, and thesurface of another pole being fixed to said second yoke; third andfourth plate-like permanent magnets each having surfaces of one andanother poles, separately arranged in said second gap in the seconddirection, the surface of the another pole being fixed to said oppositesurface of said second yoke, and the surface of the one pole being fixedto said one surface of said third yoke, said first, second, third andfourth plate-like permanent magnets supplying magnetic fluxes to saidyokes to generate first and second magnetic fields across said first andsecond gaps, respectively, in the first direction; a firstelectro-magnetic coil extending in said first and second gaps, first andsecond current components being supplied to the first electro-magneticcoil in one and opposite directions in said first and second gaps,respectively, along a third direction that is perpendicular to the firstand second directions; supporting means for supporting said firstelectro-magnetic coil to move in the second direction, said firstelectro-magnetic coil being moved in the second direction by a firstdriving force generated by interactions between the first magnetic fieldand the first current component and between the second magnetic fieldand the second current component; magnetic field generating means,arranged close to one of said first and second yokes, for generating athird magnetic field in the third direction; and a secondelectro-magnetic coil held on said supporting means to move in the firstdirection and having a section in which a third current component isflowed in the second direction, said second electro-magnetic coil beingmoved in the first direction by a second driving force generated by aninteraction between the third magnetic field and the third current,wherein said magnetic field generating means includes a fifth permanentmagnet having one and another poles arranged in the third direction andwherein said fifth permanent magnet is fixed to one of said first andsecond yokes.
 2. An apparatus according to claim 1, wherein one of saidfirst and second yokes has a recess for receiving said fifth permanentmagnet.
 3. An apparatus according to claim 1, wherein each of said firstand second gaps has a predetermined gap length in the first direction.4. An apparatus according to claim 1, wherein each of said first andsecond gaps has a predetermined gap width in the third direction.
 5. Anapparatus according to claim 1, wherein each of said first and secondgaps is defined as a substantially rectangular space.
 6. An apparatusfor generating a driving force, comprising:a first yoke, having a flatsurface, for allowing magnetic fluxes to pass therethrough; a secondyoke, having one and opposite flat surfaces, said one surface opposingone surface of said first yoke via a first gap, and arranged in a firstdirection, for allowing magnetic fluxes to pass therethrough; a thirdyoke, having one flat surface opposing the opposite surface of saidsecond yoke via a second gap, and arranged in the first direction, forallowing magnetic fluxes to pass therethrough; first and secondplate-like permanent magnets each having surfaces of one and anotherpoles, separately arranged in said first gap in a second directionperpendicular to the first direction, the surface of the one pole beingfixed to the surface of said first yoke, and the surface of another polebeing fixed to said second yoke; third and fourth plate-like permanentmagnets each having surfaces of one and another poles, separatelyarranged in said second gap in the second direction, the surface of theanother pole being fixed to said opposite surface of said second yoke,and the surface of the one pole being fixed to said one surface of saidthird yoke, said first, second, third and fourth plate-like permanentmagnets supplying magnetic fluxes to said yokes to generate first andsecond magnetic fields across said first and second gaps, respectively,in the first direction; a first electro-magnetic coil extending in saidfirst and second gaps, first and second current components beingsupplied to the first electro-magnetic coil in one and oppositedirections is said first and second gaps, respectively, in a thirddirection perpendicular to the first and second directions; supportingmeans for supporting said first electro-magnetic coil to move in thesecond direction, said first electro-magnetic coil being moved in thesecond direction by a first driving force generated by interactionsbetween the first magnetic field and the first current component andbetween the second magnetic field and the second current component;magnetic field generating means, arranged close to one of said first andsecond yokes, for generating a third magnetic field in the thirddirection; and a second electro-magnetic coil held on said supportingmeans to move in the first direction and having a section in which athird current component is flowed in the second direction, said secondelectromagnetic coil being moved in the first direction by a seconddriving force generated by an interaction between the third magneticfields and the third current, wherein said magnetic field generatingmeans includes a fifth permanent magnet having one and another polesarranged in the third direction and wherein one of said first and secondyokes has a recess for receiving said fifth permanent magnet.
 7. Asystem for optically reproducing information from an optical recordingmedium, comprising:focusing means for focusing a light beam onto saidoptical recording medium in a first direction; moving means for movingsaid focusing means in the first direction; driving force generatingmeans for generating a first driving force to convey said focusing meansin a second direction perpendicular to the first direction, said drivingforce generating means including first and second magnetic circuit meansarranged with an interval therebetween in a third directionperpendicular to the first and second direction, and conveyor means forconveying said focusing means in the second direction; each of saidfirst and second magnetic circuit means including; a first yoke, havinga flat surface, for allowing magnetic fluxes to pass therethrough; asecond yoke, having one and opposite flat surfaces, said one surfaceopposing one surface of said first yoke via a first gap, and arranged ina first direction, for allowing magnetic fluxes to pass therethrough; athird yoke, having one flat surface opposing the opposite surface ofsaid second yoke via a second gap and arranged in the first direction,for allowing magnetic fluxes to pass therethrough; first and secondplate-like permanent magnets each having surfaces of one and anotherpoles, separately arranged in said first gap in a second directionperpendicular to the first direction, the surface of the one pole beingfixed to the surface of said first yoke, and the surface of another polebeing fixed to said second yoke; third and fourth plate-like permanentmagnets each having surfaces of one and another poles, separatelyarranged in said second gap in the second direction, the surface of theanother pole being fixed to said opposite surface of said second yoke,and the surface of the one pole being fixed to said one surface of saidthird yoke, said first, second, third and fourth plate-like permanentmagnets supplying magnetic fluxes to said yokes to generate first andsecond magnetic fields across said first and second gaps in the firstdirection, respectively; and magnetic field generating means, arrangedclose to one of said first and second yokes, for generating a thirdmagnetic field in the third direction; said conveyor means including: anelectro-magnetic tracking coil having first and second sectionsextending in said first and second magnetic circuits, said first andsecond sections extending in said first and second gaps of each of saidfirst and second magnetic circuits, respectively, and first and secondcurrent components being supplied to the first and second sections inone and opposite directions in said first and second gaps in the thirddirection, respectively, and first supporting means for supporting saidelectro-magnetic tracking coil to be conveyed in the second direction,said electro-magnetic coil being conveyed in the second direction by afirst driving force generated by interactions between the first magneticfield and the first current component and between the second magneticfield and the second current component, and said moving means including;an electro-magnetic focusing coil having a section in which a thirdcurrent component is flowed in the second direction, and secondsupporting means, held on said first supporting means, for supportingsaid electro-magnetic focusing coil and said focusing means to move inthe first direction, said focusing means and said electro-magneticfocusing coil being moved in the first direction by a second drivingforce generated by interaction between the third magnetic fields and thethird current; and optical guide means for guiding light beams to saidfocusing means being conveyed, wherein said magnetic field generatingmeans includes a fifth permanent magnet having one and another polesarranged in the third direction and wherein said fifth permanent magnetis fixed to one of said first and second yokes.
 8. A system according toclaim 7, wherein one of said first and second yokes has a recess forreceiving said fifth permanent magnet.
 9. A system according to claim 7,wherein said first supporting means includesmovable means on which saidelectro-magnetic tracking coil is fixed, and mechanical guide means forguiding said movable means to be mechanically conveyed.
 10. A systemaccording to claim 9, wherein said mechanical guide means includesfirstand second guide roller mechanisms fixed to said electro-magnetictracking coil, and first and second guide rails, extending parallel toeach other in the second direction, for guiding said first and secondguide roller mechanisms, respectively.
 11. A system according to claim10, wherein said movable means includes suspending means for suspendingone of said first and second guide roller mechanisms to be deformed inthe third direction.
 12. A system according to claim 9, wherein saidmovable means has a path for passing a light beam.
 13. A systemaccording to claim 12, wherein said optical guide means includesreflecting means, fixed in said movable means, for reflecting a lightbeam toward said focusing means.
 14. A system according to claim 9,wherein said second supporting means includes a pair of leaf springsarranged parallel to each other on said movable means and having one endportion fixed to said movable means and the other end portion fixed tosaid electro-magnetic focusing coil and said focusing means.
 15. Anoptical head assembly for scanning an optical recording medium with alight beam, comprising:focusing means, having an optical axis, forfocusing a light beam onto a surface of said optical recording medium;first electro-magnetic coil means for generating a driving force formoving said focusing means in a first direction along the optical axis;supporting means, having one and the other end portion, for suspendingsaid focusing means and said first electro-magnetic coil means to movein the first direction; a first structure including a first resinportion to which said electro-magnetic coil means and one end portion ofsaid supporting means are fixed and a second resin portion to which theother end portion of said supporting means is fixed, said first andsecond resin portions each being integrally molded; and a secondstructure having a third resin portion to which a secondelectro-magnetic coil means is fixed, said third resin portion beingintegrally molded, said first structure being fixed to said secondstructure, and said first and second structures being capable of movingin a second direction, wherein said second electro-magnetic coil meansincludes a coil structure having one and the other end portionsextending in a third direction perpendicular to the first and seconddirections, wherein said second structure includes fourth and fifthresin portions fixed to one and the other end portions of said coilstructure, respectively, said fourth and fifth resin portions each beingintegrally molded, wherein said second structure further includessuspending means, fixed to said fourth resin portion, for suspending afirst guide roller mechanism to be deformed in the third direction, andwherein said second structure further includes a sixth resin portion tobe moved in the third direction upon deformation of said suspendingmeans, said suspending means and said first guide roller mechanism beingfixed to said sixth resin portion.
 16. An assembly according to claim15, wherein said sixth resin portion is mounted above said fourth resinportion with a small gap therebetween.
 17. An assembly according toclaim 15, further comprising a member, interposed in a small gap, fordamping a vibration of said sixth resin portion.
 18. An assemblyaccording to claim 15, wherein said suspending means includes a pair ofdeformable leaf springs fixed to said sixth resin portion.
 19. Anassembly according to claim 15, wherein said first structure has arecess, and said second structure has a projection projecting in thefirst direction and fitted in said recess of said first structure. 20.An apparatus for reproducing information from an optical recordingmedium, comprising:an optical head assembly for scanning said opticalrecording medium with a light beam, said assembly including: focusingmeans, having an optical axis, for focusing a light beam onto a surfaceof said optical recording medium; first electro-magnetic coil means forgenerating a driving force for moving said focusing means in a firstdirection along the optical axis; supporting means, having one and theother end portion, for suspending said focusing means and said firstelectro-magnetic coil means to move in the first direction; a firststructure including a first resin portion to which said focusing means,said electro-magnetic coil means and one end portion of said supportingmeans are fixed and a second resin portion to which the other endportion of said supporting means is fixed, said first and second resinportion each being integrally molded; and a second structure having athird resin portion to which a second electro-magnetic coil means isfixed, said third resin portion being integrally molded, said firststructure being fixed to said second structure, and said first andsecond structures being capable of moving in a second direction; andfirst and second guide roller mechanism, fixed to said second structure,for conveying said second structure; first and second guide rails,extending parallel to each other in the second direction, for guidingsaid first and second guide roller mechanisms, respectively; means forgenerating a magnetic field for causing said first electro-magnetic coilto generate a driving force; and means for generating a magnetic fieldfor causing said second electro-magnetic coil to generate a drivingforce, wherein said second electro-magnetic coil means includes a coilstructure having one and the other end portions extending in a thirddirection perpendicular to the first and second direction, wherein saidsecond structure includes fourth and fifth resin portions fixed to oneand the other end portions of said coil structure, respectively, saidfourth and fifth resin portions each being integrally molded, whereinsaid second structure further includes suspending mean, fixed to saidfourth resin portion, for suspending said first guide roller mechanismto be deformed in the third direction, and wherein said second structureincludes a sixth resin portion to be moved in the third direction upondeformation of said suspending means, said suspending means and saidfirst guide roller mechanism being fixed to said sixth resin portion.21. An apparatus according claim 20, wherein said sixth resin portion ismounted above said fourth resin portion with a small gap therebetween.22. An apparatus according to claim 21, further comprising a member,interposed in said small gap, for damping a vibration of said sixthresin portion.
 23. An apparatus according to claim 20, wherein saidsuspending means includes a pair of deformable leaf springs fixed tosaid sixth resin portion.
 24. An apparatus according to claim 20,wherein said first structure has a recess, and said second structure hasa projection projecting in the first direction and fitted in said recessof said first structure.
 25. An apparatus according to claim 20, furthercomprising flexibly deformable current supply means, having one endconnected to said second structure, for supplying a current to saidfirst and second electro-magnetic coils.
 26. An apparatus according toclaim 25, wherein said current supply means includes a pair of flexibleprint wires for cancelling a bias force in the third direction.
 27. Anapparatus according to claim 25, wherein said supporting means includesa pair of conductive leaf springs electrically connected to said currentsupply means.
 28. An apparatus according to claim 20, further comprisingmeans for detecting movement of said optical head assembly.
 29. Anapparatus according to claim 25, wherein said current supplying meansincludes a pair of lead frames, molded in the second structure, forsupplying a current to said first and second electro-magnetic coils. 30.An apparatus according to claim 20, further comprising counter weightsfixed to the second structure.
 31. An apparatus according to claim 20,wherein said second structure includes pins for rotatably supportingguide roller mechanisms.